1. Field of the Invention
This invention relates to an original reading device which scans an original while moving and reads image light obtained from the original with a photosensor.
2. Description of the Related Art
In general, in an original reading device, such as an image scanner or the like, a so-called 1:1/2 optical system is mostly adopted in which an original mounted on original-mount glass is scanned using a light source and mirrors, and the image of the original is exposed on an image sensor or a photosensitive drum. In such a 1:1/2 optical system, as shown in FIGS. 5(a) and 5(b), an original P disposed on fixed original-mount glass 100 is illuminated by a light source 101, and image light reflected by mirrors 102, 103 and 104 is focused onto an image sensor 106 including a photosensor located near an imaging lens 105. A first scanning unit 107 that includes the light source 101 and the mirror 102, and a second scanning unit 108 that includes the mirrors 103 and 104 scan the range of the original-mount glass 100 at a speed ratio of 1:1/2 along a guide rail (not shown) provided on a base frame 109 by means of a driving force from a driving source (not shown). The imaging lens 105, the image sensor 106 and the driving source are fixedly mounted on the base frame 109. As shown in FIG. 6, a signal representing an image read by the image sensor 106 is amplified by an amplifier 110, is converted into digital values by an A/D converter 111, and is transmitted to an image processing circuit 112, where image processing, such as binary coding, .gamma.-conversion or the like, is performed. The processed signal is transmitted to an external apparatus, such as a host computer, a personal computer or the like, via an interface circuit 113.
As shown in FIGS. 5(a) and 5(b), the device of this kind includes optical components, such as the first scanning unit 107, the second scanning unit 108, the lens 105, the image sensor 106 and the like, and driving-transmission components, such as a motor or the like, as principal components. The original-mount glass, a supporting member therefor, electric components and the like are mounted around the above-described principal components, and upper and lower covers are finally mounted.
In such a device, however, since the base frame is provided as a separate member, the number of components and the number of assembling processes inevitably increase, whereby it is very difficult to reduce the size of the device.